2007 Duramax brake system

[Ballistic Detailing]

I have a 2007 Duramax as soon as I start it the brake pedal sucks itself to the floor and doesn't come back up until I shut the truck off?

[Jsdirt]

Bad master cylinder, air in lines, leaking lines, calipers, wheel cylinders or ABS unit, rod fell out from between pedal and master, misadjusted brake shoes if rear drum, etc..

[Supreme Pizza]

1 hour ago, Ballistic Detailing said:

I have a 2007 Duramax as soon as I start it the brake pedal sucks itself to the floor and doesn't come back up until I shut the truck off?

 

 

   Does your truck use the hydroboost brake system?

[Jsdirt]

Most HD trucks do. If it's got the D-Max, I'd wager it's Hydroboost.

[Supreme Pizza]

5 minutes ago, Jsdirt said:

Most HD trucks do. If it's got the D-Max, I'd wager it's Hydroboost.

 

 

 

    I have repaired those types of systems before. They do not work the same way that "normal" brakes do. If you push the brakes hard, and at the same time - turn the steering wheel real hard while the tires are in deep mud - it will sheer the the input shaft off of the power steering pump. So visually everything looks fine, but the internal part of the power steering pump is not actually turning with the pulley. You have no brakes and no power steering, but no fluid leaks or anything like that.

[Jsdirt]

That wouldn't cause the pedal to drop to the floor upon startup.